1. Field of the Invention
The present invention relates to a control device which controls a synchronous motor including a reluctance motor, and a method of controlling a synchronous motor including a reluctance motor, and an electric motor vehicle control device using the same.
2. Conventional Art
In order to control such as speed and torque of a synchronous motor it is necessary to detect or estimate its magnetic pole position, and thus the speed and torque of the synchronous motor can be controlled through a current control or a voltage control thereof based on the detected or estimated magnetic pole position.
Conventionally, the magnetic pole position was detected by a position detector. However, recently a method of controlling a synchronous motor while estimating the magnetic pole position, in that a control method with magnetic pole position sensorless has been proposed which is different from the conventional method of detecting the magnetic pole position by making use of a position sensor.
For example, Takeshita, Ichikawa et al. xe2x80x9cControl of Salient Type Brushless DC Motor with Sensorless Based on Estimation of Speed Electromotive Forcexe2x80x9d (Collected Papers of Japanese Electrical Engineers Society Vol. 117-D, No. 1, 1997) proposes a method of performing speed control of a motor while estimating a speed electromotive force by making use of a motor model.
Further, JP-A-8-205578 (1996) discloses a method of detecting a salient pole characteristic of a synchronous motor based on a correlation of ripple components of a voltage vector applied to the synchronous motor through a pulse width modulation control (hereinafter referred to as PWM control) and of the corresponding motor current vector.
The art disclosed in the above paper is a method of estimating the magnetic pole position based on a difference between a current calculated on the control model and an actual motor current flowing therethrough, and has a feature that a control system can be formed only through control calculations in a controller.
Further, since the art disclosed in JP-A-8-205578 (1996) uses general PWM signals which control a voltage of the synchronous motor, the method has an advantage that no additional signals for detecting the magnetic pole position are required.
Further, with the method of estimating magnetic pole position based on a difference between a current calculated from a control model and an actual motor current flowing therethrough, there was an unsolved problem that once the synchronous motor steps out on any causes, the synchronous motor may be brought into an out-of-control condition.
On the other hand, with the art disclosed in JP-A-8-205578 (1996) the magnetic pole position of the synchronous motor can always be detected by its salient pole characteristic, therefore, the synchronous motor is never brought into an out-of-control condition.
However, with the method of detecting the magnetic pole position of a synchronous motor through its salient pole characteristic, it is necessary to detect a correlation between the motor current state and the applied voltage every time when the PWM signals change.
Namely, it is necessary to detect the motor current state and to grasp the applied voltage state at least six times for one cycle of a carrier wave, for this reason there arose a problem that the calculation speed can not catch up with, if a controller of high performance is not used.
An object of the present invention is to provide a synchronous motor control device which can be produced with low cost.
Another object of the present invention is to provide a highly reliable synchronous motor control system.
One of the measures according to the present invention is to calculate, namely to estimate a magnetic pole position of the synchronous motor based on a variation amount or a variation direction of a motor current when the synchronous motor is put in a short circuited state and to control the synchronous motor based on the calculated magnetic pole position.
Other measures according to the present invention will be explained in the Detailed Description of the Preferred Embodiments.